Biomedical subjects

P Sterk

Publications and source records attributed to P Sterk.

22 records · Page 2Linked to original sources

PubMed1991

Heterogeneity and cell type-specific localization of a cell wall glycoprotein from carrot suspension cells.

EP1, an extracellular protein from carrot (Daucus carota) cell suspensions, has been partially characterized by means of an antiserum and a cDNA clone. In both embryo and suspension cultures different molecular mass EP1 proteins were detected, some of which (31, 32, 52, and 54 kilodaltons) were bound to the cell wall and released into the medium, whereas others (49, 60, and 62 kilodaltons) were more firmly bound to the cell wall and could be extracted with a salt solution. Immunoprecipitation of in vitro translation products revealed a single primary translation product of 45 kilodaltons, suggesting that EP1 heterogeneity is due to differential posttranslational modification. In seedlings organ-specific modification of EP1 proteins was observed, a phenomenon which did not persist in suspension cultures initiated from different seedling organs. In culture EP1 proteins were only found to be associated with vacuolated, nonembryogenic cells, and on these cells they were localized in loosely attached, pectin-containing cell wall material. Purified 52/54 kilodaltons EP1 proteins did not alleviate the inhibitory effect of the glycosylation inhibitor tunicamycin on somatic embryogenesis.

Journal Article↗

PubMed1991

Cell-specific expression of the carrot EP2 lipid transfer protein gene.

A cDNA corresponding to a 10-kD protein, designated extracellular protein 2 (EP2), that is secreted by embryogenic cell cultures of carrot was obtained by expression screening. The derived protein sequence and antisera against heterologous plant lipid transfer proteins identified the EP2 protein as a lipid transfer protein. Protein gel blot analysis showed that the EP2 protein is present in cell walls and conditioned medium of cell cultures. RNA gel blot analysis revealed that the EP2 gene is expressed in embryogenic cell cultures, the shoot apex of seedlings, developing flowers, and maturing seeds. In situ hybridization showed expression of the EP2 gene in protoderm cells of somatic and zygotic embryos and transient expression in epidermis cells of leaf primordia and all flower organs. In the shoot apical meristem, expression is found in the tunica and lateral zone. In maturing seeds, the EP2 gene is expressed in the outer epidermis of the integument, the seed coat, and the pericarp epidermis, as well as transiently in between both mericarps. Based on the extracellular location of the EP2 protein and the expression pattern of the encoding gene, we propose a role for plant lipid transfer proteins in the transport of cutin monomers through the extracellular matrix to sites of cutin synthesis.

Amino Acid Sequence↗

PubMed1986

Airway responsiveness to histamine or methacholine: advances in measurement and interpretation.

A number of topical aspects of histamine or methacholine inhalation tests were discussed. First, the reporting of results as the dose delivered to the mouth by the method of aerosol generation and inhalation may allow better interpretation of results between laboratories. However, this requires investigation. Second, the histamine or methacholine dose-response curve differs in asthmatics with a moderate to severe increase in airway responsiveness from asthmatics with a mild increase in responsiveness or nonasthmatics. In the latter groups, the dose-response curve is positioned to the right and has a maximal response plateau. The disappearance of this limited maximal airway narrowing in asthmatics appears to be due to added abnormalities. Third, histamine or methacholine inhalation tests provide a sensitive and specific measure of the presence of variable airflow obstruction (asthma). They are useful to validate the diagnosis when symptoms are suggestive but spirometry is normal. The symptoms of asthma are not specific, and without objective confirmation the diagnosis is frequently misjudged even by the specialist. Finally, airway hyperresponsiveness to histamine or methacholine is not diagnostic of asthma when chronic airflow limitation is present; hyperresponsiveness to isocapnic hyperventilation may be more specific.

Asthma↗

PubMedDate not supplied

Characterization of the non-specific lipid transfer protein EP2 from carrot (Daucus carota L.).

The extracellular protein EP2 was previously identified as non-specific lipid transfer protein based on its cDNA-derived amino acid sequence. Here, the purification of the EP2 protein from the medium of somatic embryo cultures is described. After two cycles of ion-exchange and gel permeation chromatography, a single silver-stained protein band with an apparent molecular mass of 10 kDa was observed on SDS-PAGE. This protein band was recognized by the antiserum raised against a EP2-beta-galactosidase fusion-protein. Employing a fluorescent phospholipid analog, it was shown that the purified EP2 protein is capable of binding phospholipids and is able to enhance their transfer between artificial membranes. Employing a gel permeation assay, it could be demonstrated that the EP2 protein is also capable of binding palmitic and oleic acid as well as oleyl-CoA. Because in plants these fatty acids are used as precursor molecules for cutin, these results are in support of the proposed role of the EP2 protein to transport cutin monomers from their site of synthesis through the cell wall of epidermal cells to sites of cutin polymerization.

Carrier Proteins↗